T wave Alternans. A Marker of Vulnerability to Ventricular Tachyarrhythmias

Abstract

Alternation of the configuration and/or duration of the repolarization wave of the electrocardiogram (ECG) — usually referred to as T wave alternans, and occasionally as ST alternans, U wave, or TU wave alternans — is seen under diverse experimental and clinical conditions (1,2). Interest in repolarization alternans is attributed to the hypothesis that it may reflect underlying dispersion of repolarization in the ventricle, a well-recognized electrophysiolgic substrate for reentrant ventricular tachyarrhythmias (3–6). Although overt T wave alternans in the ECG are not common, in recent years digital signal-processing techniques capable of detecting subtle degrees of T wave alternans have suggested that the phenomonem may be more prevalent than recognized and could represent an important marker of vulnerability to ventricular tachyarrhythmias (7–9). This report provides a brief review of the experimental and clinical conditions associated with T wave alternans and the electrophysiologic basis that links the phenomenon to ventricular vulnerability. Preliminary observations on a recently developed noninvasive technique to detect subtle T wave alternans will also be discussed (10).

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